1. Field of the Invention
The present invention relates to a method for controlling an apparatus for controlling a cutting position of a web member in a web cutting unit and a device therefor.
2. Prior Art
A conventional web rotary printing press is shown in FIGS. 8A, 8B and 8C.
In the drawings, a web member 1 is firstly folded along a centerline in a longitudinal direction and then cut. Each cut web piece is folded along a centerline in a transverse direction.
As shown in FIG. 8A through FIG. 8C, a web member 1 is printed by a printing unit in a rotary printing press, dried, and then cut and folded by a folding unit.
The web member 1 is fed from a compensation roller 3 to a drag roller 4 by a guide roller 2. The web member 1 is folded along a centerline in a longitudinal direction by a triangle former 5 located in a downstream side. The folded web member 1 is fed to a cutting cylinder 8 through a lead roller 6 and a nipping roller 7.
The web member 1 is cut and folded in a centerline along a transverse direction after passing the cutting cylinder 8 and the folding cylinder 9 before passing a gripping cylinder 10. Then, each piece of cut web member 1 is discharged from a conveyor 11.
On the web member 1, the same printing image such as a picture pattern 12 is continuously printed. The web member 1 should be correctly cut along a boarder line between the both adjacent picture patterns 2.
However, due to some unstable factors, for example, physically unevenness of the web member 1 and a rotational unbalance and variable load of mechanical parts, control accuracy of a cutting position is reduced.
In order to improve the control accuracy of the cutting position, various devices for controlling a cutting position, so called as cut-off-control devices, have been developed.
As one of the devices for controlling a cutting position, it has been known a device for controlling a cutting position by adjusting a compensating roller 3 forwardly/rewardly in accordance with a difference between a pulse signal generated with respect to each cutting length by a cutting reference signal generator 13 mounted on the cutting cylinder 8 and a signal generated by a detecting head 14 positioned at an upper portion of the drag roller 4 for detecting each picture pattern 12.
In an above described control device for controlling an apparatus for controlling a cutting position in a web rotary printing press, the control device is switched on/off simultaneously with a cylinder in the printing press is attached/detached. In such a moment, tensile force of the web member 1 is varying so that a position of the compensating roller 3 is displaced from an original printing position. Therefore, in order to print picture patterns on a web again, cutting is not operated at a correct position until the compensating roller 3 is returned to the original printing position. It has to wait for a time and waste a large amount of printing materials.
For example, as shown in FIGS. 7A, 7B and 7C, the smaller the rotational speed of the printing press (revolution number per unit time) becomes, the smaller a tensile value of the web member 1 becomes. The larger the rotational speed of the printing press becomes, the larger the tensile value of the web member 1 becomes. When the rotational speed of the printing press becomes constant, the tensile value becomes stable. However, the cylinder of the printing press is pulled out and pushed back in the case when the rotational speed of the printing press is at the predetermined speed. If the apparatus for controlling a cutting position is switched on during an interval between the cylinder being rotated at a constant speed and the cylinder of the printing press being pulled out, and during an interval between the cylinder of the printing press being pushed back and the cylinder being rotated at a constant speed, a position of the compensating roller 3 is largely displaced due to varying tensile value of the web member 1. In the case where the printing press is intermitted and restarted, the position of the compensating roller 3 can not be quickly returned to a position where the cylinder of the printing press can be rotated at the constant speed. Thus, a large amount of printing material such as pieces of web incorrectly cut is wasted.
Therefore, the position of the compensating roller 3 is manually adjusted in an interval as shown in a bi-directional arrow in FIG. 7A so as to cut the web member 1 quickly on a correct boarder line.
A purpose of the present invention is to resolve the above drawbacks and to provide a control device for controlling an apparatus for controlling a cutting position of a web cutting unit in a printing press wherein the control device is switched ON/OFF in accordance with the rotational speed of the printing press or the tensile force of the web in an actual printing operation.